By way of example, and shown in FIG. 1, a conventional magnetic tape drive 5, comprises a rectangular shaped housing 11, an opening 14 defined therein for accepting a removable tape cartridge 20, a pair of spindle motors 10a and 10b, mounted therein, and a permanently mounted rotatable take-up reel 15. First spindle motor 10a is adapted for accepting the take-up reel while the second motor 10b is adapted for accepting the removable tape cartridge 20. Generally, the tape drive 5 further includes a head assembly 25 positioned intermediate the take-up reel 15 and the tape cartridge 20. The head assembly 25 is further positioned along a tape path 30, defined by a plurality of tape guide rollers 35. In the tape drive shown in FIG. 1, the tape path is defined by six rollers 35.
Although not shown in FIG. 1, tape drive 5 also includes a buckling mechanism 36, shown in FIG. 2, for "buckling", or attaching a take-up leader 17 with a cartridge leader 37. Typically, the buckling mechanism 36 is mounted to the drive 5 at a position intermediate the take-up reel 15 and the cartridge 20. When the tape cartridge 20 is not inserted into the drive 5, the buckling mechanism engages the take-up leader 17. The take-up leader 17 is a thin strip of polyester film e.g. Mylar, attached to the take-up reel 15. The cartridge leader is defined at the end of the data storage tape wound within the cartridge 20. As the cartridge 20 is inserted into tape drive 5, the buckling mechanism 36 releases take-up leader 17 and urges the take-up leader 17 to buckle with the cartridge leader 37.
The process of buckling tape leaders is known. For example, commonly assigned U.S. patent application Ser. No. 08/666,854, now U.S. Pat. No. 5,769,346, entitled "TAPE BUCKLING MECHANISM FOR SINGLE REEL CARTRIDGE TAPE RECORDING" describes tape leader buckling process and is therefore incorporated herein by reference.
Typically, the thickness of the leaders and the thickness of the magnetic data storage tape are not the same, i.e. the leader is thicker than data storage tape. Thus, as the leaders and tape are spooled onto a take-up reel, the take-up leader 17 length and the cartridge leader 37 length must add up to a specific length so as to minimize a condition known as "radial runout" at the take-up reel. Radial runout occurs when the cumulative length of the take-up leader and the cartridge leader, when buckled, is not equivalent to the circumference of the take-up reel hub or a multiple thereof. This condition is best illustrated in FIG. 3, which provides a magnified view of the buckled leaders 18 and tape 40 wound around the take upon reel hub 15a. As shown, the cumulative length of the buckled leaders 18, is greater than the circumference of the take-up reel hub 15a. The net effect of radial runout is that the stack of wound tape 40 becomes asymmetrical. As shown in FIG. 3, the radius on one half of the tape stack, represented by R1, is less that the radius on the other half, represented by R2. Radial runout leads to non-constant tape speed. Consequently, servo control and overall drive performance may be degraded.
Unfortunately, a consequence of fixing the cumulative length of the take-up leader and the cartridge leader to avoid radial runout, is that the take-up leader 17 may have a length which is excessively longer than the tape path, as shown in FIG. 4. This creates the possibility of the take-up leader becoming disengaged from the buckling mechanism during shipment or anytime the tape cartridge is not inserted. For example, a counter clockwise rotation, represented by the arrow D1, of take-up reel 15 would create slack in the take-up leader 17, which may cause the take-up leader to disengage from the buckling mechanism 97.
Thus, there remains an unsolved need for a take-up reel locking mechanism for preventing the take-up reel from rotating when a tape cartridge is not inserted into the tape drive.